We already know that coffee can improve your mood, reduce headaches, control blood sugar, and may help decrease your risk of colon cancer. Other research suggests it may help with memory recall and that it can increase energy expenditure (good news for those trying to lose weight), and that it may help ease the severity of asthma attacks. However, this is the first study that's ever demonstrated a relationship between coffee consumption and lifespan.

Researchers from the National Institute of Health analyzed the coffee-drinking habits of 400,000 people over a 13-year period, making it the largest study ever of the relationship between coffee and health. Starting in 1995, the researchers collected information from questionnaires filled out by respondents between the ages of 50 and 71 who were members of the American Association of Retired People (AARP). They followed the respondents until 2008, by which point, 52,000 had died.

Ultimately, the researchers found that the respondents who drank coffee regularly also smoked more, ate more red meat than the non-coffee drinkers, consumed fewer fruits and vegetables, exercised less regularly, and drank more alcohol than the non-coffee drinkers. That may sound a bit counterintuitive—after all, those are all behaviors we tend to associate with a lower quality of health. But when controlled for those risks, the researchers found that the more coffee a person drank, the less likely she or he was to die from heart disease, respiratory disease, stroke, or diabetes (but not cancer). Overall, men who drank anywhere from two to six cups of coffee regularly were 10 percent less likely to die over the course of the study, while women who drank the same amount were 15 percent less likely to die. So what does this mean? Is your morning cup of coffee literally keeping you alive? Not quite, says nutrition expert and author Amy Hendel.

"When it comes to associational findings, I think it's better to have a healthy dose of skepticism and wait for follow-up studies," she says.

The lead author of the study, Neal D. Freedman, told the New York Times that the study shows only an association between coffee consumption and lower risk for disease, so this study doesn't prove that increasing your intake of coffee will lead to better health.

There are also other variables to consider that could affect the results, says Hendel. "Caffeine itself is an antioxidant, and because of America's coffee habit, coffee is the No. 1 source of antioxidants in the current American diet, which could be at play in the results of the study."

Gender and lifestyle habits may also play a role, Hendel suggests. "Women may have other healthier behaviors that contribute to the overall observation, and female hormones may also come into play," she says.

Because epidemiological studies like this one can be confounded by different variables, it's hard if not impossible to pinpoint a reason as to why the coffee drinkers in the study lived longer than the non-coffee drinkers. Ultimately, it's important to realize that this study doesn't prove that coffee causes you to live longer, nor will drinking three cups of coffee per day erase the effects of long-term bad habits, such as smoking daily or drinking heavily.

So go ahead, indulge in that third cup of coffee (I probably will!). Just don't forget to follow it up with a healthy diet and active lifestyle.